1. Field of the Invention
The invention relates to a communication system for communicating data by using an interface comprising an upper layer and a lower layer, an information processing apparatus, an output apparatus, a control method, and a memory medium.
2. Related Background Art
Hitherto, a PC parallel interface added with a plurality of modes for providing a high speed bidirectional communication between devices has been defined in IEEE 1284. In IEEE 1284, however, a protocol called a xe2x80x9ctransport protocolxe2x80x9d for a Point-to-Point link is not defined. In IEEE 1284.4, a Point-to-Point protocol regarding several layers locating at intermediate stages between a physical interface and an application layer is designated. Such a protocol has functions and characteristics of a transport layer and a session layer in the OSI model. Further, a method of performing a bidirectional communication as a data communication between a host and a printer on the basis of IEEE 1284.4 has been proposed.
IEEE 1284.4 is a packet protocol to simultaneously transmit and receive a plurality of information (data and control information) by using one Point-to-Point link connected between two devices. The protocol, however, provides a flow control and a multiplexing service at a basic transport level instead of control information (control command) of the device. Multiplexed logical channels are independent and even if a certain channel is closed, the other channels are not influenced. Although the protocol presumes that it is operated on the IEEE 1284 interface, it can be operated on another Point-to-Point interface.
When an IEEE 1284.4 error occurs, however, the side which detects the error occurrence has to transmit an Error command specified in IEEE 1284.4 and an Exit command specified in IEEE 1284.4 to the communication partner side, receive an ExitReply command specified in IEEE 1284.4, and finish the IEEE 1284.4 mode. To resume the communication by IEEE 1284.4, the side which detected the error has to finish the communication once by IEEE 1284.4 and start the communication again by an Init command specified in IEEE 1284.4.
It is not guaranteed that the transmission and reception of the commands in an error occurring situation succeed and there is also a case where the side which detected the error has to wait for the ExitReply command permanently.
In an output apparatus having a function which does not use a bidirectional function, it the cause of the IEEE 1284.4 error is that the bidirectional function is not used during the operation of IEEE 1284.4, the ExitReply command is never issued from the output apparatus.
Among output apparatuses having an automatic switching apparatus of the IEEE 1284.4 mode and the IEEE 1284 mode (generally, referred to as a Centronics), as for the output apparatus which operates in the IEEE 1284 mode at the time of turn-on of a power supply, if the cause of the IEEE 1284.4 error is a turn-off and a re-turn-on of the power supply, the Error command and Exit command are erroneously recognized as a part of print data in the IEEE 1284.4 mode.
To solve the above problems, it is an object of the invention that when an error occurs in an upper layer (for example, IEEE 1284.4), an output apparatus is allowed to certainly recognize the error by using a predetermined command (for example, a device ID request specified in IEEE 1284.4) of a lower layer.
To accomplish the above object, according to the invention, there is provided a communication system comprising an information processing apparatus and an output apparatus for outputting in accordance with data from the information processing apparatus, wherein
the information processing apparatus and the output apparatus can communicate data by using an interface constructed by an upper layer and a lower layer, and
when the information processing apparatus detects an error at the time of the data communication using the upper layer, a predetermined command specified in the lower layer is used for allowing the output apparatus to recognize the occurrence of the error.
According to the invention, there is provided an information processing apparatus which can communicate data with an output apparatus by using an interface comprising an upper layer and a lower layer, wherein
the apparatus has issuing means for issuing a predetermined command specified in the lower layer in order to allow the output apparatus to recognize the occurrence of an error when the error is detected at the time of the data communication using the upper layer.
According to the invention, there is provided an output apparatus which can communicate data with an information processing apparatus by using an interface comprising an upper layer and a lower layer, wherein
the apparatus has control means for performing a resetting process when a predetermined command specified in the lower layer is received at the time of the data communication using the upper layer.
According to the invention, there is provided a control method of an information processing apparatus which can communicate data with an output apparatus by using an interface comprising an upper layer and a lower layer, wherein
the method has an issuing step of issuing a predetermined command specified in the lower layer in order to allow the output apparatus to recognize the occurrence of an error when the error is detected at the time of the data communication using the upper layer.
According to the invention, there is provided a control method of an output apparatus which can communicate data with an information processing apparatus by using an interface comprising an upper layer and a lower layer, wherein
the method has a control step of performing a resetting process when a predetermined command specified in the lower layer is received at the time of the data communication using the upper layer.
According to the invention, there is provided a machine-readable memory medium which stores a control program of an information processing apparatus which can communicate data with an output apparatus by using an interface comprising an upper layer and a lower layer, wherein
the control program has an issuing step of issuing a predetermined command specified in the lower layer in order to allow the output apparatus to recognize the occurrence of an error when the error is detected at the time of the data communication using the upper layer.
According to the invention, there is provided a machine-readable memory medium which stores a control program of an output apparatus which can communicate data with an information processing apparatus by using an interface comprising an upper layer and a lower layer, wherein
the control program has a control step of performing a resetting process when a predetermined command specified in the lower layer is received at the time of the data communication using the upper layer.